The primary visual cortex is critically important in human visual perception. Since the way in which the visual cortex functions in vision is determined by the complex set of connections between its neural elements, the long range objective of these studies is to gain an understanding of the developmental factors that produce these connections by analyzing genetic mutants that alter visual cortical development. To this end, we have undertaken an analysis of the visual cortex of the reeler mutant mouse which has a stereotyped abnormality in cell position in cortical structures, including the visual cortex. We have used this mutant to analyze the role of neuronal position in the formation of cell-to-cell connections in the visual cortex. To provide a framework for the analysis of the eller mutant, we have analyzed the retinotopic organization of the striate and extrastriate visual regions of the cortex in the mouse and the laminar distribtuion of neurons with particular receptive field characteristics in te striate cortex. We have also studied the receptive field properties of a set of neurons that project from the visual cortex to the superior colliculus, and determined that the functional characteristics of these cells in normal and reller are not significantly different. Thus the connections that determine the functional characterisitcs of these neurons are properly established in reeler, even though they are in markedly abnormal positions in the visual cortex. In the present application, we propose to continue our analysis of the visual cortex of the reeler mutant mouse in an attempt to determine 1) whether the functional characteristics of neurons that require more precision in the number and location of their afferent connections are altered when the neurons are in abnormal positions; 2) whether the cells of origin and the patterns of termination of the affarent and efferent connections of the striate and extrastrate visual cortical regions are altered by the abnormalities in laminar position that characterize reeler cortex; 3) whether cell death plays a role in the development of the normal visual cortex, or in removing abnormally connected neurons from the reeler visual system; 4) whether the radial glia that are thought to guide neurons in their migration to the developing cortical plate are altered morphologically in reeler. These studies will emlploy the techniques of microelectrode recording for mapping receptive fiels, neuronal transport of tracer substances to define visual system connections, and immunhistofluorescence to study radial glia.